Recognising all contributions (big and small and non-tutorial)

[hexylena]

@shiltemann and I were discussing #2980 / #2973 and we were brainstorming ways that we could help track all of the contributions someone makes on the GTN!

• They could register it manually (maybe from a predefined list of categories)
• We should link to the PRs / Issues they made, that's a nice way to say "look, here's everything they worked on" (but it doesn't include PRs contributed to I think, just PRs they opened so, will miss some stuff)
  • Can we get a Number for this from the API 'cheaply'? Do we fetch the PR list every build (slow) or use some JS to contact the GH API (does it allow unauthenticated requests?)
• We could look through the git history to track who edited what and maybe define some paths like "_layout, _include, assets" ⇒ Website Layout & Style, "bin, .github" ⇒ "GTN Infrastructure" (but this might either require a mailmap file to get the GH usernames, or calls to the GH api

This is also related to #2015